High comp question.

[240sxdrifterS14]

Hey guys I am a bit of noob and I definately dont understand the science behind how compression works. But what I would like to know is how streetable you guys think an n/a KA would be that had 11.5:1 compression. I have a dual cam that I inherited from a friend that has single cam pistons in it, along with a whole load of other parts. What I want to know is if you all with more knowledge than I, think that on 91 crap gas the car would be a reliable dd. I would like to keep the motor but if it is something that i have to run octane booster in I think I will just sell it. Thanks for you opinions ahead of time.

[!Zar!]

When you need to run a higher octane, octane booster isn't going to even come close.

[1ZlowZ]

KAe pistons lower compression I think on a KADE to run turbo
I haven't searched but I think I read that somewhere. I guess maybe lower compression helps deal with all the pressure the turbo is putting into the engine?
I don't I'm stupid.I want info too please.

[Andrew Bohan]

sohc pistons raise compression in a dohc
dohc pistons lower compressoin in a sohc

you can run 91 octane with high comp but you have to retard the timing so much it'll feel the same as stock

with my high comp ka, i ran a mix of 91 and toluene that gave me 98 octane, and it felt a little slower than a stock SR. when i got low on gas and filled up with just 91, the engine blew 75 miles later.

maybe that's coincidence. hahah

[240sxdrifterS14]

KAe pistons lower compression I think on a KADE to run turbo
I haven't searched but I think I read that somewhere. I guess maybe lower compression helps deal with all the pressure the turbo is putting into the engine?
I don't I'm stupid.I want info too please.

You have it the other way around single cams are lower compression then dual cams, but when you mix single cam pistons with a dual cam head you raise comp. Early single cam pistons in a dual cam results in either 11.5 or 11.6:1 compression.

Still I am wondering if running this high of compression on 91 crap gas is possible with out haveing the timing super retarted. Thanks for the help.

[mr.jdm]

Octane booster does not work. In fact. It has been proven that it lowers gas mileage. They ran tests. Its a waste of money

[Andrew Bohan]

the point of octane booster is not to increase gas mileage though.

[240sxdrifterS14]

sohc pistons raise compression in a dohc
dohc pistons lower compressoin in a sohc

you can run 91 octane with high comp but you have to retard the timing so much it'll feel the same as stock

with my high comp ka, i ran a mix of 91 and toluene that gave me 98 octane, and it felt a little slower than a stock SR. when i got low on gas and filled up with just 91, the engine blew 75 miles later.

maybe that's coincidence. hahah

what was your compression. That is what I was thinking that runing high comp on pump gas would not be possible without retarding the timing. I think i am going to sell my motor.

[Andrew Bohan]

jeez i forget now. 89 and 90 pistons are different.

i was 10.5:1, or something. the lower of the two.
11.5:1 is higher than i wanted to go.

[mr.jdm]

the point of octane booster is not to increase gas mileage though.


i know that. but read a octane booster bottle next time you run across one. they claim it does in fact raise gas mileage.

[240sxdrifterS14]

jeez i forget now. 89 and 90 pistons are different.

i was 10.5:1, or something. the lower of the two.
11.5:1 is higher than i wanted to go.

The lower single cam pistons are 11.1:1 or something like that I think. But yah if you ran that crazy with the lower of the two I will probably just sell this motor, it's got a crap load of work done to it, but just not something for me. Not to hop and the bandwagon but you really just cant beat an sr for realiabilty and fun.

[UNISA JECS]

jeez i forget now. 89 and 90 pistons are different.

i was 10.5:1, or something. the lower of the two.
11.5:1 is higher than i wanted to go.

1989 used both 8.6:1 and 9.1:1 pistons.

1990 used I believe only 9.1:1 pistons.

[Andrew Bohan]

i'm talking about when you put them in a dohc

[UNISA JECS]

Just did a search supposidly this is from ASAD from FA so if thats true you can pretty much count on it being correct info.

Early 8.6:1 KA-E pistons into KA-DE gives 11.1:1
Later 9.1:1 KA-E pistons into KA-DE gives 11.6:1

[Andrew Bohan]

mine must have been 11.1 then

[Koopa Troopa]

You can mix gasoline and kerosene to make a higher octane fuel.

However with the right ECU and tuning you shouldn't have any problems making good power with a high compression KA on 91 octane.